1. Field of the Invention
The present invention relates to an aqueous ink, particularly to an aqueous ink suitable for ink-jet recording. The present invention relates also to an ink-jet recording method, an ink-jet recording apparatus, an ink cartridge, a recording unit, and a coloring material.
2. Related Background Art
Various types of printers are known as image-forming apparatuses, including thermal transfer printers, laser beam printers, dot impact printers, and ink-jet printers. Of these printers, the ink-jet printer is constructed so as to eject ink droplets toward a recording medium like a paper sheet and deposit the droplets thereon. The ink-jet recording system is attracting attention in recent years owing to its capability to form a full color image with high image quality at a low cost. The ink-jet recording method includes thermal ejection methods utilizing bubbling of a liquid upon heating for ink ejection, and piezo ejection methods employing a piezo element.
In the ink-jet recording, usually an aqueous ink is used as the ink. The aqueous ink usually contains as a colorant an aqueous dye such as, for example, acid dyes, direct dyes, and basic dyes. Hence, the ink-jet recording may give rise to such a problem that the recorded images are not satisfactory in their water resistance and ozone resistance disadvantageously.
On the other hand, the ink prepared by dispersing a pigment in an aqueous medium forms images with higher image fastness or durability such as water resistance and light fastness than the aqueous ink employing a water-soluble dye as the colorant. However, the pigment dispersion ink is generally inferior in color of the images such as an optical density and chroma of the images, to the aqueous ink. Further, the image printed with such a pigment dispersion ink is not sufficient in fixation to the recording medium surface, so that the paper face may be soiled with the pigment when the images are rubbed with a finger and the image areas may be blurred when they are marked with a marking felt-tip pen. Hence, the images are not sufficient in the rub resistance and marking resistance.
To solve the above problem, various techniques for improvement of the water resistance and fixability of recording images are proposed, such as incorporation of a resin in the ink, and use of a dye-colored resin as the coloring agent. Japanese Patent Application Laid-Open No. 10-140057 discloses the incorporation of a film-forming resin and non-film-forming resin in the ink to improve the fixability and ink ejection stability. Japanese Patent Application Laid-Open No. 11-29732 discloses the incorporation of fine particulate film-forming polymer in the ink to obtain images having high rub resistance and high water resistance.
The inventors of the present invention have investigated the above prior art techniques. An ink containing a colorant 2001 and a particulate resin 2003 dispersed separately as shown in FIG. 2A does not improve sufficiently the ozone resistance and the water resistance of the formed images. This is because, on application of the ink on a recording medium 2005, the colorant 2001 is distributed among the particulate resin 2003 on the surface of the recording medium 2005 as shown in FIG. 2B, thereby preventing approach of the resin particles to retard the formation of a film on the recording medium, and leaving the colorant remaining on the recording medium surface without sufficient incorporation of the colorant into the film.
Japanese Patent Application Laid-Open No. 5-255567 discloses use of an aqueous dispersion of a coloring resin to enhance the water resistance and rub resistance of the images. Japanese Patent Application Laid-Open No. 55-139471 discloses an ink which employs colored particles prepared by dispersing a dye in an aqueous medium containing a vinyl resin latex dispersed therein and further dispersing the dye in the resin particle, for example, by heat treatment. Japanese Patent Application Laid-Open No. 62-95366 discloses that an ink is prepared by dissolving a polymer and an oil dye in a water-insoluble organic solvent, emulsifying the resulting solution to obtain polymer particles containing the dye therein and then incorporating the polymer particles in the ink. As a result of the studies by the inventors of these techniques, the formed images are found to be deteriorated in terms of the color tone and transparency or clarity although the rub resistance and the ozone resistance thereof are improved.
An object of the present invention is to provide an ink which is able to form recorded images having improved water resistance and improved ozone resistance that are not achievable by the conventional aqueous inks employing a water-soluble dye as the coloring agent and which is able to provide recorded images with improved fixability, improved color developability and improved ozone resistance that are not achievable by the conventional dispersion type inks employing a pigment as the coloring agent; in particular, to provide an ink which can be widely used as a recording liquid for recording apparatus like ink-jet recording and give recorded images having satisfactory rub resistance and ozone resistance and being excellent in color development and image transparency.
Another object of the present invention is to provide an ink-jet recording method which gives ink-jet images having high rub resistance and ozone resistance, and high color developability and high transparency, which are not simultaneously achievable by the conventional recording method.
Still another object of the present invention is to provide an ink-jet recording apparatus and ink-jet recording unit which are able to give ink-jet recorded images with excellent rub resistance and ozone resistance and with satisfactory color developability and high image transparency.
A further object of the present invention is to provide an ink cartridge which can be used for forming recorded images with satisfactory rub resistance and ozone resistance and with excellent color developability and image transparency.
A still further object of the present invention is to provide a coloring material which can be used for forming recorded images with satisfactory rub resistance and ozone resistance and with excellent color developability and image transparency.
The inventors of the present invention have investigated the reason for the lowered color developability and the lowered transparency or clarity of the images which are formed with the conventional ink containing a coloring resin composed of a colored film-forming resin for improvement of the rub resistance. According to the investigation, the colorant 3001 is in a state of aggregation in the resin particle 3003 in the ink as shown in FIG. 3A. When the ink is applied onto a recording medium 3007, the resin 3003 forms a film 3005, and the aggregated colorant particles 3001 are localized in the resin film 3005 as shown in FIGS. 3B and 3C. It thus has turned out that the light scattering is caused by the colorant particles and the color tint of the colorant is changed by the absorption wavelength shift due to the aggregation of the colorant, and as a result, the color developability and the image transparency are lowered. The present invention is based on the such finding.
According to one aspect of the present invention, there is provided an aqueous ink comprising a colored resin dispersed therein, the colored resin comprising a film-forming resin and a colorant dispersed in a monomolecular state in the film-forming resin.
According to another aspect of the present invention, there is provided an ink-jet recording method comprising a step of ejecting an aqueous ink comprising a colored resin dispersed therein through an orifice in correspondence with a recording signal to deposit the ejected ink onto a recording medium, the colored resin comprising a film-forming resin and a colorant dispersed in a monomolecular state in the film-forming resin.
According to still another aspect of the present invention, there is provided an ink cartridge comprising an ink container containing the above-mentioned ink.
According to further aspect of the present invention, there is provided a recording unit comprising an ink container containing an aqueous ink, and a head for ejecting the ink through an orifice in correspondence with a recording signal, the aqueous ink comprising a colored resin dispersed therein, and the coloring resin comprising a film-forming resin and a colorant dispersed in a monomolecular state in the film-forming resin.
According to still further aspect of the present invention, there is provided a coloring material comprising colored resin particles comprising a film-forming resin and a colorant dispersed in a monomolecular state in the film-forming resin.